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Supplementary Information SI-I Experimental

Making of Room Temperature TiO2 photoanodes: The TiO2 paint was prepared using tertiary butyl

alcohol (tBA) and water as solvents. Small amount of dilute acid (pH ~2) was also added to this 5

mixture. Various weight ratios of tBA: TiO2 were examined for optimization. After adding the desired

amount of TiO2 to this solvent system it was continuously stirred for several hours to get a viscous

paste. The TiO2 paint thus formed was coated on FTO/glass substrates as well as ITO-PET substrates

using doctor blading technique. Application of the paint on the substrate by using a paint brush was

also examined. Both the substrates were properly cleaned prior to paint application. TiO2 layers with 10

different thicknesses were realized by multiple application of the paint. After drying the films at room

temperature they were soaked in 0.5mM N719 solution. Solar cells made with top electrode (Pt

catalyst on FTO) and iodide-tri-iodide electrolyte were then made and tested for energy conversion

efficiency and solar cell parameters. Impedance measurements were also carried out to examine the

various resistances involved in the equivalent circuit. 15

Materials and Methods: Commercially available TiO2 (Degussa, P25) was procured and used for

making the solar paint. The N719 dye and Fluorine doped SnO2 (FTO) electrodes (sheet resistance 15

ohm/square) were procured from Solaronix Co. The electrolyte used was 0.5 M 1, 2-dimethyl-3-propyl

imidazolium iodide, 0.05 M LiI, 0.05 M I2, and 0.5 M 4-tert-butylpyridine in acetonitrile/valeronitrile

(v/v 1:1). The I–V characteristics were measured using a solar simulator (Newport) at 100 mW/cm2 (1 20

sun AM 1.5). Standard Silicon solar cell (SER NO. 189/PVM351) from Newport, USA was used as

reference cell. The measurements of incident-photon-to-current conversion efficiency (IPCE) were

done using Quantum Efficiency Setup (Newport Instruments). Diffused Reflectance Spectroscopy

(DRS, Jasco V-570 spectrophotometer), Field emission scanning electron microscopy (FE-SEM

HITACHI S4800) and Electrochemical Impedance Spectroscopy (EIS, Autolab PGSTAT30 (Eco-25

Chemie)) were used to characterize the samples. The impedance measurements were performed at

room temperature.

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Supplementary Information SI-II Figure SI-II shows the actual images and the FE-SEM images of the TiO2 paint as the tBA: TiO2 ratio

is varied from low (2) to high (8). The (a1, a2), (b1, b2), (c1, c2), (d1, d2) cases correspond to the

values of the ratio as 2, 4, 6, and 8, respectively. 5

10

15

20

25

30

It can be seen that when the ratio is small (Figure SI-II (a2)) the film does not have a uniform texture

and agglomerates are seen. It is also clear from Figure (SI-II (a1)) that the paste formed is too thick to 35

be properly blade-coated or painted on a substrate. Also there is no proper necking between the

particles (See SI-III (a)). When the ratio is increased, the film formed is of good quality maintaining

proper porosity for dye loading as well as rendering good necking between the particles (Figure SI-II

(b2)). The slurry/paste formed using this ratio forms a uniform coating on the side walls of glass vial

a 1 a 2

b 1

d 2 d 1

c 2c 1

b 2





when tilted as seen in Figure SI-II (b1). When the ratio is further increased a uniform film is formed

but there is slight decrease in film porosity (see Figure SI-II (c2)). As seen from Figure SI-II(c1) this

paste also forms a coating on the walls of glass vial when tilted. When the concentration of tBA is very

high compared to TiO2 the film shows scattered clusters as seen in Figure SI-II (d2). Also the slurry

formed is not homogeneous and it separates out from the solvent as seen in Figure SI-II (d1). 5





Supplementary Information SI-III Supplementary information SI-III shows the FE-SEM images at a higher resolution. 5

10

15

20

FE-SEM images of all four cases with tBA : TiO2 ratio (b1) 2, (b2) 4, (b3) 6 and (b4) 8 25

30

35

40

Magnified FE-SEM images for all the four cases with tBA: TiO2 ratio 2 (a), 4 (b), 6 (c) and 8 (d).





Supplementary Information SI-IV 5

10

15

20

25

Percent (%) Transmittance data as a function of film thickness for tBA: TiO2 ratio 4: 1

300 400 500 600 700 800

5

10

15

20

%T

Wavelength (nm)

3m 8m 12m 15m 17m





Supplementary Information SI-V 5

10

15

20

25

30

35

(A) I-V Data of large area solar paint and (B) Image of Al metal deposited large area solar cell made

from solar paint.

40

0.0 0.2 0.4 0.6 0.80

2

4

6

8

10

A

Voc

= 0.74 V

Jsc

= 9.55 mA / cm2

FF = 43 %Eff. = 3.1%

Cu

rren

t D

ensi

ty (

mA

/cm

2 )

Voltage (V)

Cell Area 2.8cm2

B


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